المتغيرات والثوابت في البرمجة

Variables and Constants

• Variables are named storage locations in memory that can hold different values during program execution.
• Constants are named storage locations in memory that hold values that cannot be changed during program execution.
• Variables can store numerical, character, or other types of data.
• Variable contents can be altered at any time.
• Constants hold fixed data values that cannot changed during program execution.
• Examples of constants include a circle's area calculation where pi (π) is a constant value of 3.14.

Differentiating Variables and Constants

• Variables and constants are differentiated by their mutability, variables can change, constants cannot.

Variable Naming Rules

• Variable names must not start with a number.
• Variable names must begin with a letter.
• Variable names are case-sensitive.
• The variable name starts with a letter.
• Variable names cannot include spaces or special symbols.
• Variable names must not be reserved words in C#.
• It is possible to use the underscore character between the words

Data Types

• Data type declarations allocate memory space for the specified type of data.
• Common data types include integers, float, and strings.
• NET allocates memory based on the data type.
• There are signed integers to store both positive and negative numbers.
• There are unsigned integers which store only positive values.

Integer Data Types

• byte: Stores integers from 0 to 255 (1 byte).
• sbyte: Stores integers from -128 to 127 (1 byte).
• short: Stores integers from -32,768 to 32,767 (2 bytes).
• ushort: Stores integers from 0 to 65,535 (2 bytes).
• int: Stores integers from -2,147,483,648 to 2,147,483,647 (4 bytes).
• uint: Stores integers from 0 to 4,294,967,295 (4 bytes).
• long: Stores integers from -9,223,372,036,854,775,808 to 9,223,372,036,854,775,807 (8 bytes).
• ulong: Stores integers from 0 to 18,446,744,073,709,551,615 (8 bytes).

Floating Point Data Types

• float: Stores floating-point numbers(4 bytes, 7 decimal digits).
• double: Stores floating-point numbers (8 bytes, 16 decimal digits).
• decimal: Stores floating-point numbers (16 bytes, 29 decimal digits).

Declaring Variables

• Variable declaration involves specifying the data type and name.

Datatype VariableName;
int streetNum;

• Multiple variables can be declared in one line.

int ax, bx, cx;

Strings and Chars Data Types

• string: Stores a sequence of text from multiple characters.
• char: Stores a single character (2 bytes).

string address;

Boolean Data Type

• bool: Stores either true or false values.

bool bx;

• The default value is false.

Working with Variables

• Assigning a value is called assignment.

Assigning Values to Variables

• Assign a value to a variable

int xx=90;

• Assign a value after declaring

int xx;
xx=90;

How Computers Handle Variables

• Assignment statements assign value.
• When you use the same name on both sides the computer computes the right side and overrides the left side.

Variable Scope

• Local Variables declared inside a method.
• Model Variables declared in the model, where they are kept until disposal.
• Global Variables are available to all Models.

Local Variables

• Declared inside a particular procedure or block of code.
• Use is restricted to the block in which declaration took place.

Model Variables

• Declared within the Form creation part.
• Visible to all actions within the form.
• Persist in memory until the form closes.

Global Variables

• Usable in every model.
• Declared inside a class.

Constants

• Constants values cannot be changed while the program is running.
• Two types: those defined within C#.NET and those defined by the programmer.
• To declare constants use const data type such as float.

Programmer Defined Constants

• These are defined within the project to be used as project specific constants.

Data Type Conversions

• C# provides type conversion between variables.
• A value placed between quotation marks "" will always be text.
• C#.Net treats text differently than numbers.

Parsing

• Use Parsed data when user inputs data is automatically stored as text (strings).

int xx;
xx= int.Parse(textBox1.Text) +int.Parse(textBox2.Text);
textBox3.Text = xx.ToString();

• Used when converting strings to numeric values example converting temperature from Celsius to Fahrenheit.

Converting Numbers to Strings

• Use .ToString();

Label1.Text = My_salary.ToString();

Numeric Data Conversions

• Type must be converted when converting between short and long, you can convert shorts into longs because it is going from smaller to larger bytes.
• Errors will occur when going from larger type like Long into Short.
• Operations for converting follow the Convert class.

Conversion Functions

• Convert.ToInt16
• Convert.ToInt32
• Convert.ToInt64
• Convert.ToDecimal
• Convert.ToSingle
• Convert.ToDouble
• Convert.ToByte

B1= Convert.ToDecimal(A1);
B2 = Convert.ToInt32(A2);